Why decussation of pyramids

Ants, crabs, squid, worms, sponges, jellyfish, butterflies, scallops, and snails all fall into this category. And—interestingly, none of these species exhibit the crossing pattern that you mention. Decussations are unique to vertebrates. Some invertebrates, such as sponges, have no known nervous tissue. Slightly more advanced invertebrates, those with radial body plans think, jellyfish , have a diffuse "nerve net," but no central nervous system to decussate.

Bilateral invertebrates, however, tend to have a large collection of neurons near the front of the body the brain , and a nerve cord or cords that runs the length of the animal. The primitive brain of bilateral invertebrates is found above dorsal to their mouths, just like ours is. Beyond that, however, something very different happens.

In humans and in other vertebrates sharks, crocodiles, frogs, owls, kangaroos… , the spinal cord runs along the back-side of the body. We did not observe any changes in the cortex of the precentral gyrus and other cortical regions as other authors. Focal decrease in the FA value on brain DTI maps found in the course of cortico-spinal tracts, hyperintensity in T2-weighted images in the lateral cortico-spinal tracts of the thoracic spinal cord indicated axonal degeneration of the pyramidal tracts in our patient.

Wang et al. To the best of our knowledge there have been few studies on MRI changes in the spinal cord in patients with different types of MND.

The asymmetry of pyramidal tract lesions closely corresponded to the clinical findings asymmetry of paresis. According to Agosta et al. The authors emphasize the importance of neuro-imaging in PLS recognition. A good quality, high-resolution MRI is able to visualize changes in pyramidal tracts at the level of the spinal cord and DTI study at the level of the brain in PLS patients.

Standard CT or MRI evaluation does not demonstrate gross structural nervous system changes in ALS, so conventional neuro-imaging techniques have provided little insight into the pathophysiology of this disease.

Advanced neuro-imaging techniques—such as structural MRI, diffusion tensor imaging and proton magnetic resonance spectroscopy—allow evaluation of alterations of the nervous system in ALS. These alterations include focal loss of grey and white matter and reductions in white matter tract integrity, as well as changes in neural networks and in the chemistry, metabolism and receptor distribution in the brain. Given their potential for investigation of both brain structure and function, advanced neuro-imaging methods offer important opportunities to improve diagnosis, guide prognosis, and direct future treatment strategies in ALS.

One of the first ALS studies to focus on the pyramidal tract in the brainstem reported decreased FA at the level of the pons and medulla in patients versus controls. By contrast, no diseaseassociated differences in FA or MD were detected in these brainstem regions in another study, although they were evident at the level of the cerebral peduncle. Reductions in brainstem levels of NAA have also been detected in patients with ALS, although no significant changes in Glx were observed.

Advanced neuro-imaging studies demonstrate structural and metabolic changes in the brainstem in ALS. DTI studies of the brainstem are subject to greater variability than are studies of other brain regions owing to decussation of fibre tracts in this region. Overall, results from 1H-MRS studies provide evidence of neuronal degeneration in the brainstem similar to that in the motor cortex. PET findings support the presence of metabolic, neuroinflammatory and reactive changes in the brainstem in ALS.

Focal atrophy of the spinal cord in ALS correlated with muscle deficits. One study also demonstrated focal FA reductions and increased radial diffusivity in dorsal spinal cord columns, which suggests involvement of spinal sensory pathway in ALS. A longitudinal study demonstrated reductions in spinal cord FA and cross-sectional area and increased MD at 9-month follow-up. MRS studies have focused on the upper cervical cord to minimize the challenges of anatomy and motion artefacts.

One study found increased myo-inositol:Cr ratios, which were not confirmed in the other MRS studies. Diffusion tensor imaging—One of the first ALS studies to focus on the pyramidal tract in the brainstem reported decreased FA at the level of the pons and medulla in patients versus controls.

By contrast, no disease-associated differences in FA or MD were detected in these brainstem regions in another study, although they were evident at the level of the cerebral peduncle. Implications of imaging findings—Advanced neuro-imaging studies demonstrate structural and metabolic changes in the brainstem in ALS.

New advances in neuroimaging techniques will enable the challenges of investigating this important nervous system structure—which is integrally involved in the pathophysiology of ALS—to be addressed [10]. A conclusion contrary to most researchers, who continue to support that ALS is a neruo-degenerative disease, and therefore has not cure. The surgery was performed in 2 stages under general anesthesia: First, supraumbilical laparotomy to remove a segment of omentum and then, cervical laminectomy at the C1-C2 and C5-C6 only in 9 cases levels.

During the laparotomy, in 36 patientsthe omentum was of poor quality; because this tissue was found thickened, pale and greasy milky spots , ovoid, rounded, and poorly vascularized. A patient had not major omentum, because he havebeen suffered colon surgery several years ago, for this reason, we obtained almost all the minor omentum. The medulla oblongata and cervical cord at C5-C6 level, was located as previously described technique. A segment of omentum was placed on the anterior piramidal decussation and bulbar pyramids , lateral and posterior surface of the medulla oblongata and fixed to the dura mater by its inner face, and into 9 patients of this group, they received an additional segment of omentum on the anterior, lateral and posterior surface of the cervical cord at C5-C6 level by spinal ALS.

In all cases, the dura matter was laxly faced and not to water seal. The nasogastric tube to receive liquid feed and hydratation. In , based on neurosurgical experiences with omental transplantation,one of us published a hypothesis about the neruodegenerative mechanisms. Hypothesis supported currently by several authors, that the neruo-degenerative process is secondary to the formation of free radicals and oxidative stress in the ischemic area; provoking an imbalance between the oxidant and anti-oxidant endogenous defenses systems, in favor of the oxidants.

Under normal biochemical and physiological conditions in any area of the brain, the levels of free radicals are controlled by enzymes such as catalase, glutatione peroxidase and various types of superoxide dismutase, among other endogenous defenses anti-oxidants which prevent the process of oxidative stress, ie.

That is, without vascular recanalization or revascularization in the ischemic zones, residual neurons no re-send axons to specific areas already establised, ie.

Whether these changes are associated with disruption to the direct cerebellar tract pathways to the motor cortex and spinal cord in ALS is uncertain. Diffusion tensor imaging was used to examine the integrity of 2 primary cerebellar pathways, the dentato-rubro-thalamo-cortical DRTC and spino-cerebellar SC tracts. Significant alterations across diffusion metrics in the DRTC proximal to the motor cortex were found in both patient groups.

Disruption to primary cerebellar tracts in PLS is therefore postulated, adding to other markers of its divergent pathogenesis from ALS [12]. Cristina Grande, et al: Gastropod mitochondrial genomes exhibit an unusually great variety of gene orders compared to other metazoan mitochondrial genome such as e. Comparative analyses with other mollusk mitochondrial genomes allowed us to describe molecular features and general trends in the evolution of mitochondrial genome organization in gastropods.

Phylogenetic reconstruction with commonly used methods of phylogenetic inference ME, MP, ML, BI arrived at a single topology, which was used to reconstruct the evolution of mitochondrial gene rearrangements in the group. Caenogastropoda and Vetigastropoda are sister taxa, as well as, Patellogastropoda and Heterobranchia. The gene order of the Vetigastropoda might represent the ancestral mitochondrial gene order for Gastropoda and we propose that at least 3 major rearrangements have taken place in the evolution of gastropods: one in the ancestor of Caenogastropoda, another in the ancestor of Patellogastropoda, and one more in the ancestor of Heterobranchia [13].

The monophyly of Pulmonata has been accepted by many authors based on some morphological characters like the streptoneuran inervation of the cephalic tentacles, and the lack of rhinophoric nerve present in opisthobranchs and pyramidellids. The procerebrum is formed of small and large neuronal cells, and because it links the peripheral tentacular structures with the central nervous system, an olfactory function has been assumed.

The cerebral gland is a neuronal structure associated with the cerebral ganglia. New molecular data reject Pulmonata as a natural group based on both nuclear and mitochondrial data.

In this study, we have included representatives of all major lineages within pulmonates Systelommatophora, Basommatophora, Ellobiidae, and Stylommatophora. All these lineages independently reject the definition of pulmonates as a natural group in all the performed analyses.

Stylommatophora land snails is a monophyletic group, in agreement with previous morphological studies, and it is recovered as the sister group to all other heterobranchs studied. Our results provide new insights into land colonization by heterobranch gastropods. The transition to a land lifestyle was accompanied by a variety of refined morphological and physiological modifications.

As a result, land snails and slugs constitute a well-defined group of pulmonates with several morphological synapomorphies in the cephalic tentacles, kidney, and central nervous system, as well as in several aspects of their ontogeny.

Previous phylogenetic hypotheses had suggested that the transition to land was a rather derived event in the history of pulmonates. Our molecular phylogeny instead supports a different scenario in which gastropod land colonization, and subsequent radiation was an early and significant event in the evolution of Heterobranchia [13]. Despite several intensive studies, the driving force of torsion remains to be determined. Although torsion was traditionally believed to be driven by contraction of the retractor muscle connecting the foot and the shell, some recent reports cast doubt on that idea.

Here, we report that torsion is accompanied by left—right asymmetric cell proliferation in the mantle epithelium in the limpet Nipponacmea fuscoviridis. We confirmed that the blocking was brought about through failure of the activation of cell proliferation in the right-hand side of the mantle epithelium, while the retractor muscle apparently developed normally. Rengasayee Veeraraghavan et al: In addition to the structural substrate, conduction is also modulated by dynamic functional changes.

Primarily, these dynamics result from the interplay between the strength of the excitatory impulse the source and the electrical load represented by the tissue it must excite the sink. As an activation wavefront spreads through the myocardium, the amount of source available per unit mass of tissue is determined by its excitability, whereas the balance between source and sink is determined by the curvature of the wavefront and its interaction with the architecture of the myocardium: intercellular coupling, fiber orientation, rotational anisotropy, branching tissue geometry.

Since local excitability in tissue is dynamically modulated by changes in the shape and duration of action potentials, mismatch between source and sink can arise locally and dynamically, creating a functional substrate for arrhythmogenic conduction defects. Pathophysiological gap junction remodeling and fibrosis can exacerbate source-sink mismatch and thereby the propensity for arrhythmias. For a more detailed discussion of source-sink mismatch, the reader is referred to the in depth review of electrotonic conduction by Drs.

Kleber and Y. Rudy [15]. The introduction of anterolateral cordotomy led to much discussion of the manner in which the spinothalamic tract crosses the cord. There are 2 views: one is that the fibres cross transversely; the other is that they cross diagonally, taking several segments to cross.

In this paper we present the evidence that the fibres cross transversely and also theoretical reasons why they cannot be crossing diagonally.

The first investigator to make use of anterolateral cordotomy to study the anatomy of the spinal cord was Foerster.

He wrote that he had had seven cases with a sensory level at the segment below the incision. He concluded that the fibres cross the cord within one to one-and-a-half segments above their cell bodies and that when this result is not obtained the incision has not been deep enough. Later, Foerster and Gagel published a series of cases in which there were nine autopsies.

Kuru, who studied with Foerster, had detailed histological material from 10 cases of cordotomy. His conclusions supported Foerster and Gagel. White and colleagues found that an analgesic level to within one segment of the incision was rarely obtained and they concluded that this was due to the diagonal crossing of the fibres.

He reported a case in which the incisions into the cord were at T4 or T5 with hypoalgesia at T5 level. In he reported 20 cases of cordotomy carried out at C2; the analgesia was up to the territory of the fifth cranial nerve in 2 of them. One of the best papers on this subject is that published by White and colleagues in In this paper, as in many others, the reader needs to distinguish the level of sensory loss obtained immediately after the operation from levels seen when some return of sensibility had taken place.

Bohm reported that, in 28 of 35 cases of unilateral cervical cordotomy, there was complete analgesia extending to one segment below the incision. In 10 of these patients the incision was at C1—2 and in 12 it was between C3 and C4. On reading the literature, one finds that adequate attention has not been given to the relationship between the surgical incision and the fibres passing from the anterior commissure and through the anterior horn.

Yet this relationship provides an important clue showing that the fibres cross the cord transversely [16]. Welniarz Q et al: The cortico-spinal tract CST plays a major role in cortical control of spinal cord activity.

In particular, it is the principal motor pathway for voluntary movements. Here, we discuss: i the anatomic evolution and development of the CST across mammalian species, focusing on its role in motor functions; ii the molecular mechanisms regulating cortico-spinal tract formation and guidance during mouse development; and iii human disorders associated with abnormal CST development.

A comparison of CST anatomy and development across mammalian species first highlights important similarities. In particular, most CST axons cross the anatomical midline at the junction between the brainstem and spinal cord, forming the pyramidal decussation. Reorganization of the pattern of CST projections to the spinal cord during evolution led to improved motor skills. Studies of the molecular mechanisms involved in CST formation and guidance in mice have identified several factors that act synergistically to ensure proper formation of the CST at each step of development.

These latter disorders result in altered midline crossing at the pyramidal decussation or in the spinal cord, but spare the rest of the CST. Careful appraisal of clinical manifestations associated with CST malformations highlights the critical role of the CST in the lateralization of motor control [17].

Mohamed-Mounir El Mendili et al: The mechanisms underlying the topography of motor deficits in spinal muscular atrophy SMA remain unknown. Patients were scored on manual muscle testing and functional scales. Spinal cord was imaged using 3T MRI system. Radial distance RD and cord cross-sectional area CSA measurements in SMA patients were compared to those in controls and correlated with strength and disability scores.

CSA measurements revealed a significant cord atrophy gradient mainly located between C3 and C6 vertebral levels with a SCA rate ranging from 5. The midsagittal T2-weighted image from the end of C2 to the end of C7 vertebra was used to measure the cervical spine c-spine length mm. Sex, age at cervical MRI, number and location of cervical spinal cord lesions, c-spine length, and diagnoses were analyzed against the outcome measures of CASA and C2 and C7 slice segmental areas.

Cervical magnetic resonance imaging 11 years after the accident demonstrated atrophy and hyperintense lesions at the C6 and C7 levels in the cervical cord with an abnormal alignment of the vertebrae. In the neck flexion position, an anterior shift of the cervical cord was evident. The DTI images depict axonal fiber orientation, enable quantification of diffusion characteristics along the spinal cord, and have the potential to demonstrate the connectivity of cord white matter tracts.

Because of the high sensitivity to motion of diffusion-weighted magnetic resonance imaging and the small size of the spinal cord, a fast imaging method with high in-plane resolution was developed. Images were acquired with a single-shot EPI technique, named ZOOM-EPI zonally magnified oblique multislice echo planar imaging , which selects localized areas and reduces artefacts caused by susceptibility changes between soft tissue and the adjacent vertebrae.

Cardiac gating was used to reduce pulsatile flow artefacts from the surrounding cerebrospinal fluid. Voxel resolution was 1. Both the mean diffusivity MD and the fractional anisotropy FA indices of the cervical spinal cord were measured.

The FA index demonstrated high anisotropy of the spinal cord with an average value of 0. The high axial resolution allowed preliminary evaluation of fiber connectivity using the fast-marching tractography algorithm, which generated traces of fiber paths consistent with the well-known cord anatomy [21]. C Chien et al: Measures for spinal cord atrophy have become increasingly important as imaging biomarkers in the assessment of neuro-inflammatory diseases, especially in neuro-myelitis optica spectrum disorders.

The most commonly used method, mean upper cervical cord area, is relatively easy to measure and can be performed on brain MRIs that capture cervical myelon.

Measures of spinal cord volume eg, cervical cord volume or total cord volume require longer scanning and more complex analysis but are potentially better suited as spinal cord atrophy measures. This study investigated spinal cord atrophy measures in a cohort of healthy subjects and patients with aquaporin-4 antibody seropositive neuro-myelitis optica spectrum disorders and evaluated the discriminatory performance of mean upper cervical cord crosssectional area compared with cervical cord volume and total cord volume.

Previous studies have demonstrated that SCA can be associated with longer disease duration and more severe disability and can potentially indicate poor prognosis in NMOSD. It is measured as the crosssectional area of the spinal cord at the level between the C2 and C3 vertebrae.

Although longitudinally extensive transverse myelitis predominantly affects the cervical and upper thoracic spinal cord, the lower thoracic and lumbar cord in patients with NMOSD is often affected as well. Hence, the main disadvantage of MUCCA is that though it can be easily obtained and measured, it covers only a very small fraction of the spinal cord.

Christopher P. These studies have demonstrated that whole-cord atrophy and atrophy of the lateral and posterior WM columns are not observed in the lower cord. Although the cervical cord has a predilection for demyelinating WM lesions, tissue loss within WM lesions does not have a significant influence on local cord Atrophy. What Is 'Semantic Bleaching'? How 'literally' can mean "figuratively". Literally How to use a word that literally drives some pe Is Singular 'They' a Better Choice?

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